Orthopaedic bearing and method for making the same

ABSTRACT

An orthopaedic bearing includes a ceramic component having a polymer composite secured thereto. A method of making an orthopaedic bearing is also disclosed.

CROSS REFERENCE

Cross reference is made to copending U.S. patent application Ser. No.______ entitled “Orthopaedic Bearing and Method of Making the Same”(Attorney Docket No. 265280-76607, DEP-5269DIVI) and Ser. No. ______entitled “Orthopaedic Bearing and Method of Making the Same” (AttorneyDocket No. 265280-74908, DEP-5269USA), both of which are assigned to thesame assignee as the present application, are filed concurrentlyherewith, and are hereby incorporated by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to implantable orthopaedicbearings and methods of making the same.

BACKGROUND

Implantable orthopaedic bearings, such as glenoid bearings, aretypically made with polyethylene. One type of polyethylene commonly usedin the fabrication of such bearings is Ultra-High Molecular WeightPolyethylene (UHMWPE). Certain characteristics of UHMWPE may be enhancedby exposing it to radiation such as gamma radiation. In particular,exposing UHMWPE to predetermined doses of radiation crosslinks theUHMWPE thereby increasing its wear resistance. Techniques forcrosslinking, quenching, or otherwise preparing UHMWPE are described innumerous issued U.S. patents, examples of which include U.S. Pat. No.5,728,748 (and its counterparts) issued to Sun, et al, U.S. Pat. No.5,879,400 issued to Merrill et al, U.S. Pat. No. 6,017,975 issued toSaum, et al, U.S. Pat. No. 6,242,507 issued to Saum et al, U.S. Pat. No.6,316,158 issued to Saum et al, U.S. Pat. No. 6,228,900 issued to Shenet al, U.S. Pat. No. 6,245,276 issued to McNulty et al, and U.S. Pat.No. 6,281,264 issued to Salovey et al. The disclosure of each of theseU.S. patents is hereby incorporated by reference.

SUMMARY

According to one aspect of the disclosure, an orthopaedic bearingincludes a metallic component having a polymer composite securedthereto. The polymer composite may include a non-crosslinked layer ofpolymer and a crosslinked layer of polymer. The non-crosslinked layer ofpolymer may be positioned between the metallic component and acrosslinked layer of polymer.

The crosslinked layer of polymer may have an articulating surfacedefined therein.

The crosslinked layer of polymer may include gamma irradiated polymer.

Both layers of polymer may include polyethylene. The polyethylene may beUHMWPE.

The metallic component may include a solid metal body with a porouscoating disposed thereon.

The metallic component may include a porous metal body.

In lieu of a non-crosslinked layer of polymer, a layer of polymer whichhas been crosslinked to a lesser degree than the crosslinked layer maybe used.

According to another aspect of the disclosure, a method of making anorthopaedic bearing includes securing a polymer composite to a metalliccomponent. The polymer composite may be molded to the metalliccomponent. The polymer composite may be compression molded to themetallic component.

The polymer composite may include a non-crosslinked layer of polymer anda crosslinked layer of polymer. The non-crosslinked layer of polymer maybe positioned between the metallic component and a crosslinked layer ofpolymer.

An articulating surface may be molded into the crosslinked layer ofpolymer.

The crosslinked layer of polymer may include gamma irradiated polymer.

Both layers of polymer may include polyethylene. The polyethylene may beUHMWPE.

Both layers of polymer and the metallic component may be molded in asingle molding process. The layers of polymer may first be molded to oneanother, and thereafter molded to the metallic component in a subsequentmolding process. The non-crosslinked layer of polymer may first bemolded to the metallic component, with the crosslinked layer of polymerbeing molded to the non-crosslinked layer of polymer in a subsequentmolding process.

A polymer preform may be used as the starting material for one or bothof the crosslinked layer of polymer and the non-crosslinked layer ofpolymer.

A polymer powder may be used as the starting material for one or both ofthe crosslinked layer of polymer and the non-crosslinked layer ofpolymer.

The metallic component may include a solid metal body with a porouscoating disposed thereon.

The metallic component may include a porous metal body.

In lieu of a non-crosslinked layer of polymer, a layer of polymer whichhas been crosslinked to a lesser degree than the crosslinked layer maybe used.

The above and other features of the present disclosure will becomeapparent from the following description and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the accompanying figuresin which:

FIG. 1 is a perspective view of an implantable glenoid bearing;

FIG. 2 is a cross sectional view taken along the line 2-2 of FIG. 1;

FIG. 3 is a perspective view of the metallic component of the glenoidbearing of FIG. 1; and

FIG. 4 is a cross sectional view similar to FIG. 2, but showing anotherembodiment of an implantable glenoid bearing.

DETAILED DESCRIPTION OF THE DRAWINGS

The present disclosure relates to implantable orthopaedic bearings andmethods of making the same. Such bearings may be utilized in a number ofjoint replacement or repair procedures such as surgical proceduresassociated with the shoulders, hips, knees, ankles, knuckles, or anyother joint. As such, although the following description illustrates oneexemplary type of bearing (i.e., a glenoid bearing), it should beappreciated that the invention is not limited to glenoid bearings andmay find applicability in the design of any type of orthopaedic bearing.

Referring now to FIGS. 1-3, there is shown an implantable orthopaedicbearing 10 such as a one-piece glenoid bearing 12 for implantation intoa glenoid of a patient (not shown). The glenoid bearing 12 has a polymercomposite 14 secured to a metallic component 16. The polymer composite14 has an articulating or bearing surface 18 on which a natural orprosthetic component bears. For example, a natural or prosthetic humeralhead (not shown) bears on the articulating surface 18 when the glenoidbearing 12 is implanted into a patient. The metallic component 16 has akeel 22 defined therein. The keel 22 is inserted into a surgicallyformed slot (not shown) in the glenoid surface of the patient. The keel22 may be press fit or held in place by the use of bone cement. Itshould be appreciated that the metallic component 16 may be embodiedwith attachment features other than the keel 22. For example, themetallic component 16 may be embodied with one or more pegs.

The polymer composite 14 has a number of polymer layers 24, 26. Thepolymer layer 24 of the composite 14 is constructed with a materialwhich possesses mechanical properties favorable for use in theconstruction of the articulating surface 18 (e.g., enhanced wear andoxidation resistance). The polymer layer 26, on the other hand, isconstructed of a material which possesses mechanical propertiesfavorable for use in securing the polymer layer 24 to the metalliccomponent 16. It should be appreciated that, as used herein, the term“layer” is not intended to be limited to a “thickness” of materialpositioned proximate to another similarly dimensioned “thickness” ofmaterial, but rather is intended to include numerous structures,configurations, and constructions of material. For example, the term“layer” may include a portion, region, or other structure of materialwhich is positioned proximate to another portion, region, or structureof differing material.

As used herein, the term “polymer” is intended to mean any medical gradepolymeric material which may be implanted into a patient. A specificexample of such a polymer is medical grade polyethylene. The term“polyethylene”, as defined herein, includes polyethylene, such as apolyethylene homopolymer, high density polyethylene, high molecularweight polyethylene, high density high molecular weight polyethylene,ultrahigh molecular weight polyethylene, or any other type ofpolyethylene utilized in the construction of a prosthetic implant. Amore specific example of such a polymer is medical grade UHMWPE. Theterm “polymer” is also intended to include both homopolymers andcopolymers. The term “polymer” also includes oriented materials, such asthe materials disclosed in copending U.S. patent application Ser. No.09/961,842 entitled “Oriented, Cross-Linked UHMWPE Molding forOrthopaedic Applications”, which was filed on Sep. 24, 2001 by King etal., which is hereby incorporated by reference, and which is owned bythe same assignee as the present application.

The term “polymer” is also intended to include high temperatureengineering polymers. Such polymers include members of thepolyaryletherketone family and the polyimide family. Specific members ofthe polyaryletherketone family include polyetherketoneetherketoneketone,polyetheretherketone, and polyetherketone.

In one exemplary embodiment, a polymer composite 14 is utilized in whichthe polymer layer 24 is made with a crosslinked polymer, whereas thepolymer layer 26 is made with a non-crosslinked polymer. In a morespecific exemplary embodiment, the polymer utilized in the constructionof both polymer layers 24, 26 of the polymer composite 14 ispolyethylene. One particularly useful polyethylene for use in theconstruction of the polymer layers 24, 26 is UHMWPE.

As described above, a polymer may be crosslinked by, for example,exposure to radiation such as gamma radiation. As such, the polymerlayer 24 (i.e., the crosslinked polymer layer) of the polymer composite14 of this exemplary embodiment may be fabricated by exposing thepolymer layer 24 to gamma radiation. Such exposure may be in theexemplary range of 10-150 KGy. The polymer layer 26 (i.e., thenon-crosslinked polymer layer) of the polymer composite 14 of thisexemplary embodiment is not exposed to such gamma radiation. In a morespecific exemplary embodiment, the polymer layer 24 (and hence thearticulating surface 18 formed therein) is constructed of a crosslinkedpolyethylene such as crosslinked UHMWPE, whereas the polymer layer 26 isconstructed of a non-crosslinked polyethylene such as a non-crosslinkedUHMWPE.

In another exemplary embodiment, a polymer composite 14 is utilized inwhich the polymer layer 24 is made from a polymer which has beencrosslinked to a first degree, whereas the polymer layer 26 isconstructed from a polymer which has been crosslinked to a seconddegree. Specifically, the polymer layer 26 is made with a polymer whichhas been crosslinked to a lesser degree than the polymer utilized tomake the polymer layer 24. One way to vary the degree in which a polymeris crosslinked is to vary the dose of radiation to which it is exposed.In a general sense, the greater the dose of radiation to which thepolymer is exposed, the greater the degree in which the polymer iscrosslinked. As such, in regard to the polymer composite 14 of thisexemplary embodiment, the polymer layer 24 is exposed to a first dose ofgamma radiation, whereas the polymer layer 26 is exposed to a second,different dose of gamma radiation. In a more specific exemplaryembodiment, the dose of gamma radiation to which the polymer layer 26 isexposed is less than the dose of radiation to which the polymer layer 24is exposed.

Hence, in a specific implementation of the polymer composite 14 of thisexemplary embodiment, the first polymer layer 24 may be made from apolyethylene such as UHMWPE which has been exposed to a first dose ofgamma radiation. The second layer 26, on the other hand, may be madewith a polyethylene such as UHMWPE which has been exposed to a second,different dose of gamma radiation. It should be appreciated that thedose of gamma radiation to which the polyethylene of the polymer layer26 is exposed is less than the dose of radiation to which thepolyethylene of the polymer layer 24 is exposed. It should beappreciated that the polymer layer 26 of this exemplary polymercomposite 14, although crosslinked to some degree, still possesses manyfavorable mechanical characteristics to facilitate securing the morehighly crosslinked polymer layer 24 to the metallic component 16.

As alluded to above, the material from which the polymer layer 26 ismade may include polymers other than polyethylene. For example, thepolymer layer 26 may be made with poly methyl methacrylate (PMMA). Alonga similar line, although crosslinked polymers are believed at present toprovide superior wear resistance and oxidation resistance for thearticulating surface in orthopaedic implants, new materials may bedeveloped in the future with improved properties. Accordingly, thepresent invention is not limited to any particular material, and mayencompass newly developed materials, unless a particular material isexpressly set forth in the claims.

Referring in particular now to FIG. 3, the metallic component 16 has ametal body 28 which is made from an implantable metal such as stainlesssteel, cobalt chrome, titanium, or the like. The metal body has a porouscoating 30 disposed thereon. The porous coating 30 facilitates bonyingrowth to the backside 32 and keel 22 of the metallic component 16.Moreover, in the case of when bone cement is used, the porous coating 30enhances fixation to the backside 32 and keel 22 of the metalliccomponent 16. The porous coating 30 is also disposed on the surface 34on which the polymer composite 14 is molded. During the molding process,the polymer layer 26 is forced into or otherwise interdigitates with theporous coating 30 thereby enhancing the mechanical connectiontherebetween. One type of porous coating which may be used as the porouscoating 30 is Porocoat® Porous Coating which is commercially availablefrom DePuy Orthopaedics of Warsaw, Ind.

The components of the one-piece glenoid component 12 (i.e., the metalliccomponent 16, the polymer layer 24, and the polymer layer 26) may beassembled by use of a number of different techniques. One exemplarymanner for doing so is by use of compression molding techniques. Forexample, the metallic component 16, the material from which the polymerlayer 24 is to be made, and the material from which the polymer layer 26is to be made may be placed in a mold with one another. Thereafter, thecomponents are compression molded to one another under processparameters which cause the material from which the polymer layer 26 ismade to be molten and fused to the material from which the polymer layer24 is made thereby creating the polymer composite 14. At the same time,the material from which the polymer layer 26 is made is mechanicallysecured to the metallic component 16 by the compression molding process.As described above, the molten polymer layer 26 interdigitates with theporous coating 30 of the metallic component 16 when molded thereto. Itshould also be appreciated that the mold may be configured to not onlyfuse the components to one another, but also form the articulatingsurface 18 into the polymer composite 14.

Other methods of compression molding the one-piece glenoid bearing 12are also contemplated. For example, in lieu of contemporaneously moldingthe components of the one-piece glenoid component 12 (i.e., the metalliccomponent 16, the polymer layer 24, and the polymer layer 26) to oneanother in a single molding process, multiple molding processes may beemployed. For instance, the polymer composite 14 may be formed in afirst molding process by compression molding the material from which thepolymer layer 24 is to be made and the material from which the polymerlayer 26 is to be made to one another. Thereafter, the polymer composite14 and the metallic component 16 may be molded to one another in aseparate mold process.

In another multi-step molding process, the material from which thepolymer layer 26 is to be made may be molded to the metallic component16 in a first molding process. Thereafter, in a second molding process,the material from which the polymer layer 24 is to be made is moldedonto the polymer layer 26.

The starting composite materials (e.g., polymers such as polyethylene)for use in the molding process may be provided in a number of differentforms. For example, each of the starting materials may be provided as apreform. What is meant herein by the term “preform” is an article thathas been consolidated, such as by ram extrusion or compression moldingof polymer resin particles, into rods, sheets, blocks, slabs, or thelike. The term “preform” also includes a preform “puck” which may beprepared by intermediate machining of a commercially available preform.Polymer preforms such as polyethylene preforms may be provided in anumber of different pre-treated or preconditioned variations. Forexample, crosslinked or non-crosslinked (e.g., irradiated ornon-irradiated) preforms may be utilized. Such preforms may be treatedto eliminate (e.g., re-melting or quenching) or stabilize (e.g., theaddition of vitamin E as an antioxidant) any free radicals presenttherein. Alternatively, the preforms may not be treated in such amanner.

The starting composite materials (e.g., polymers and copolymers) mayalso be provided as powders. What is meant herein by the term “powder”is resin particles. Similarly to as described above in regard topreforms, powders may be provided in a number of different pre-treatedor preconditioned variations. For example, crosslinked ornon-crosslinked (e.g., irradiated or non-irradiated) powders may beutilized.

It should be appreciated that the starting composite materials (e.g.,the preforms or powders) may be “pre-irradiated”, “pre-treated toeliminate or stabilize free radicals”, or otherwise preconditioned priorto use thereof. In particular, it may be desirable for a manufacturer ofprosthetic bearings to purchase material (e.g. polyethylene) which hasbeen irradiated (or otherwise crosslinked), pre-treated to eliminate orstabilize free radicals, or otherwise preconditioned by a commercialsupplier or other manufacturer of the material. Such “out-sourcing” ofpreconditioning processes is contemplated for use in the processesdescribed herein.

In regard to fabrication of a bearing 12 having a polymer composite 14in which the polymer layer 24 is made of crosslinked polymer and theother polymer layer 26 is made of non-crosslinked polymer, a preform ofpolymer which is non-crosslinked (i.e., non-irradiated) may bepositioned in a mold between a preform of crosslinked polymer (i.e.,pre-irradiated) and the metallic component 16. Thereafter, the metalliccomponents and the two preforms are compression molded under processparameters which cause the non-crosslinked preform of polymer to be (i)molten and fused to the preform of crosslinked polymer, and (ii) moltenand mechanically secured to the metallic component 16. It should also beappreciated that during such a molding process, the articulating surface18 is formed in the resultant polymer composite 14. Moreover, duringsuch a molding process, the polymer associated with the layer 26 isinterdigitated with the porous coating 30 of the metallic component 16.In an exemplary implementation of this process, a preform of acrosslinked polyethylene such as crosslinked UHMWPE is compressionmolded to a preform of a non-crosslinked polyethylene such asnon-crosslinked UHMWPE, which is, in turn, molded to the metalliccomponent 16. As alluded to above, such a fabrication process may beperformed in a number of different molding steps. For example, the twopreforms may first be molded to one another, with the resultant polymercomposite then being molded to the metallic component 16 in a subsequentmolding process. Alternatively, the non-crosslinked polymer preform mayfirst be molded to the metallic component 16, with the crosslinkedpolymer preform being molded to the non-crosslinked layer in asubsequent molding process.

Such a polymer composite 14 (i.e., the polymer layer 24 made ofcrosslinked polymer and the polymer layer 26 made of non-crosslinkedpolymer) may also be fabricated by the use of polymer powders. Forexample, polymer powder which is non-crosslinked (i.e., non-irradiated)may be placed in a mold between a preform of crosslinked polymer (i.e.,pre-irradiated) and the metallic component 16. Thereafter, thecomponents are compression molded under process parameters which causethe non-crosslinked polymer powder to be (i) molten and fused to thepreform of crosslinked polymer, and (ii) molten and mechanically securedto the metallic component 16. It should also be appreciated that duringsuch a molding process, the articulating surface 18 is formed in theresultant polymer composite 14. Moreover, during such a molding process,the polymer associated with the layer 26 is interdigitated with theporous coating 30 of the metallic component 16. In an exemplaryimplementation of this process, the crosslinked preform may be providedas a crosslinked polyethylene preform such as a crosslinked UHMWPEpreform, whereas the non-crosslinked powder may be provided as anon-crosslinked polyethylene powder such as a non-crosslinked UHMWPEpowder. Similarly to as described above in regard to use of twopreforms, the fabrication process may be performed in a number ofdifferent molding steps. For example, the crosslinked preform and thenon-crosslinked powder may first be molded to one another, with theresultant polymer composite then being molded to the metallic component16 in a subsequent molding process. Alternatively, the non-crosslinkedpolymer powder may first be molded to the metallic component 16, withthe crosslinked polymer preform being molded to the non-crosslinkedlayer in a subsequent molding process.

In regard to fabrication of a bearing 12 having of a polymer composite14 in which the polymer layer 24 is made of a polymer which has beencrosslinked to a first degree and the other polymer layer 26 is made ofa polymer which has been crosslinked to a second, lesser degree, apreform of polymer which is crosslinked to the second (lesser) degreemay be positioned in a mold between a preform of the polymer which hasbeen crosslinked to the first (greater) degree and the metalliccomponent 16. Thereafter, the metallic components and the two preformsare compression molded under process parameters which cause the lessercrosslinked preform of polymer to be (i) molten and fused to the preformof greater crosslinked polymer, and (ii) molten and mechanically securedto the metallic component 16. It should also be appreciated that duringsuch a molding process, the articulating surface 18 is formed in theresultant polymer composite 14. Moreover, during such a molding process,the polymer associated with the layer 26 is interdigitated with theporous coating 30 of the metallic component 16. In an exemplaryimplementation of this process, a preform of polyethylene such as UHMWPEwhich is crosslinked to a first degree is compression molded to apreform of polyethylene such as UHMWPE which is crosslinked to a second,lesser degree, which is, in turn, molded to the metallic component 16.In a similar manner to as described above, this fabrication process mayalso be performed in a number of different molding steps. For example,the two preforms may first be molded to one another, with the resultantpolymer composite then being molded to the metallic component 16 in asubsequent molding process. Alternatively, the lesser crosslinkedpolymer preform may first be molded to the metallic component 16, withthe greater crosslinked polymer preform being molded to the lessercrosslinked layer in a subsequent molding process.

Such a polymer composite 14 (i.e., a polymer layer 24 constructed of apolymer which has been crosslinked to a first degree and a polymer layer26 constructed of a polymer which has been crosslinked to a second,lesser degree) may also be fabricated by the use of polymer powders. Forexample, polymer powder which is crosslinked to the second (lesser)degree may be placed in a mold between a preform of polymer crosslinkedto the first (greater) degree and the metallic component 16. Thereafter,the components are compression molded under process parameters whichcause the lesser crosslinked polymer powder to be (i) molten and fusedto the preform of greater crosslinked polymer, and (ii) molten andmechanically secured to the metallic component 16. It should also beappreciated that during such a molding process, the articulating surface18 is formed in the resultant polymer composite 14. Moreover, duringsuch a molding process, the polymer associated with the layer 26 isinterdigitated with the porous coating 30 of the metallic component 16.In an exemplary implementation of this process, a powder of polyethylenesuch as UHMWPE which is crosslinked to a first degree is compressionmolded to a preform of polyethylene such as UHMWPE which is crosslinkedto a second, lesser degree. Similarly to as described above in regard touse of two preforms, the fabrication process may be performed in anumber of different molding steps. For example, the greater crosslinkedpreform and the lesser crosslinked powder may first be molded to oneanother, with the resultant polymer composite then being molded to themetallic component 16 in a subsequent molding process. Alternatively,the lesser crosslinked polymer powder may first be molded to themetallic component 16, with the greater crosslinked polymer preformbeing molded to the lesser crosslinked layer in a subsequent moldingprocess.

It should also be appreciated that although the composites 14 haveherein been described as having two layers, other compositeconfigurations are also contemplated. For example, the polymer composite14 may be configured to include several alternating layers of materialssimilar to the materials used in regard to the two-layer compositesdescribed above. For instance, the polymer composite 14 may beconfigured to include several (i.e., more than two) layers ofalternating crosslinked and non-crosslinked UHMWPE. It should also beappreciated that more than two different material types may also be usedin the construction of the composite. For example, a third material typemay be used as an adhesion promoter between two layers (or between alayer and the underlying (e.g., metallic) component).

Moreover, it may be desirable to use vacuum molding for some materials.For example, vacuum molding may be preferred where one or more of thelayers include a non-quenched material.

Other methods of securing the two polymer layers can be used for someapplications. For example, instead of melt-fusion, mechanical interlockscan be used in some applications. With the choice of appropriatematerials and processes, mechanical interlocks between polymer layersmay provide an interface with adequate mechanical and dynamicproperties. For an application relying upon mechanical interlocks, it isbelieved that mechanical interlocking with adequate interfacial strengthcan be achieved by providing a layer of polymer 26 having a porousstructure of a high-temperature engineering polymer, such as one fromthe polyaryletherketone family or the polyimide family, and by controlof process parameters. In such an application, a crosslinked UHMWPElayer may be used for the polymer layer 24 for the articulating surface.The crosslinked UHMWPE layer 24, in the form of a powder or preform, maybe compression molded to the layer 26 of porous high temperatureengineering polymer under a temperature that will melt at least aportion of the UHMWPE layer, so that UHMWPE melts into and fills some ofthe pores of the high temperature engineering material; when this UHMWPEmaterial solidifies, the two polymer layers will be mechanically bondedtogether. The compression molding can be done at a temperature highenough to melt the UHMWPE layer but below the melting point of thepolymer layer of polymer 26. The high temperature may be localized atthe interface of the layers 24, 26. The porous structure may have asolid section.

The polymer layer 26 of porous high temperature engineering polymer maycomprise an engineering polymer such as polyetheretherketone,polyetherketone, polyetherketoneetherketoneketone or polyimide. Thesematerials are biocompatible and are able to withstand the processingtemperature for UHMWPE without significant deformation. Preforms can bereadily fabricated from these raw materials using conventionalprocessing techniques. Although it is expected that these polymermaterials will be useful as one of the polymer layers when relying upona mechanical interlock, the present invention is not limited to thesematerials unless the claims expressly call for them. The presentinvention may also encompass newly developed polymers, unless aparticular polymer is expressly set forth in the claims.

In addition, although the mechanical interlock that secures the twopolymer layers together can be formed by compression molding the twopolymer layers together, methods such as hot isostatic pressing may beused to secure the two layers of polymer 24, 26 together with amechanical interlock. In addition, as new polymer materials aredeveloped, new methods of securing the polymer layers together may alsobe developed. Accordingly, the present invention is not limited to anyparticular method of securing the polymer layers together, and mayencompass newly developed materials and securing means, unless aparticular material or process is expressly set forth in the claims.

Referring now to FIG. 4, there is shown another exemplary embodiment ofthe one-piece glenoid bearing 12. The glenoid bearing 12 of FIG. 4 isessentially the same as the bearing 12 of FIGS. 1 and 2 except for theconfiguration of the metallic component (which is designated withreference numeral 36 in FIG. 4). Specifically, in lieu of a solid metalbody with a porous coating disposed thereon, the metallic component 36of the glenoid bearing 12 of FIG. 4 has a porous metal body 38. As such,when the polymer of the polymer layer 26 is molded to the metalliccomponent 36, the polymer is interdigitated with the porous metal body38.

Prior to molding the polymer layer 26 to the porous metallic component36, a sacrificial layer of polymer (not shown) may be molded to thebackside 40 of the metallic component 36. The molding process may becontrolled to allow the sacrificial layer of polymer to penetrate apredetermined distance into the metallic component 36. As such, when thepolymer of the polymer layer 26 is molded to the front side 42 of themetallic component 36 the polymer of the polymer layer 26 is preventedfrom penetrating the entire thickness of the metallic component 36 bythe sacrificial layer of polymer.

Once the polymer layer 26 has been molded to the metallic component 36(with or without the polymer layer 24), the glenoid bearing 12 (orpartially fabricated bearing 12) the sacrificial layer of polymer isremoved by water extraction. This removes the sacrificial layer ofpolymer without disturbing the polymer layer 26 (and the polymer layer24 if present) thereby exposing the porous backside 40 of the metalliccomponent 36 (including the depth into its porous body 38 previouslyoccupied by the sacrificial layer of polymer). Such exposed portions ofthe porous body promote bony ingrowth or cement adhesion into theglenoid bearing 12 when its implanted in a manner similar to asdescribed above in regard to the porous coating 30 of the bearing 12 ofFIGS. 1-3.

It should be appreciated that any desirable type of material may be usedas the sacrificial layer of polymer. One type of such material is ameltable, high molecular weight hydrophilic polymer. A specific exampleof one such polymer is polyethylene oxide.

While the disclosure is susceptible to various modifications andalternative forms, specific exemplary embodiments thereof have beenshown by way of example in the drawings and has herein be described indetail. It should be understood, however, that there is no intent tolimit the disclosure to the particular forms disclosed, but on thecontrary, the intention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the disclosure.

There are a plurality of advantages of the present disclosure arisingfrom the various features of the apparatus and methods described herein.It will be noted that alternative embodiments of the apparatus andmethods of the present disclosure may not include all of the featuresdescribed yet still benefit from at least some of the advantages of suchfeatures. Those of ordinary skill in the art may readily devise theirown implementations of an apparatus and method that incorporate one ormore of the features of the present disclosure and fall within thespirit and scope of the present disclosure.

For example, although it has been described herein to crosslinkmaterials via irradiation, it should be appreciated that such materialsmay be crosslinked by any suitable technique. In addition, although thecrosslinked polymer or more highly crosslinked polymer is typically beused for the articulating surface of the composite with non-crosslinkedor less crosslinked polymer being used to facilitate securing thecrosslinked polymer or more highly crosslinked polymer to the metalliccomponent, there may be instances where it is desirable for thecrosslinked polymer or more highly crosslinked polymer layer to be usedto secure the non-crosslinked or less crosslinked polymer to themetallic bearing, with the latter layer being used for the articulatingsurface.

Moreover, in lieu of the of a metallic component, a ceramic componentmay be used in the fabrication of the orthopaedic bearing 10. In such acase, a porous ceramic component or porous coated ceramic component isused in lieu of the metallic component 16, with the bearing 10 beingfabricated otherwise as described herein.

1. An implantable orthopaedic bearing, comprising: a ceramic component,a non-crosslinked layer of polymer secured to the ceramic component, anda crosslinked layer of polymer secured to the non-crosslinked layer ofpolymer.
 2. The bearing of claim 1, wherein the crosslinked layer ofpolymer is molded to the non-crosslinked layer of polymer.
 3. Thebearing of claim 2, wherein the crosslinked layer of polymer comprises agamma irradiated crosslinked layer of polymer.
 4. The bearing of claim1, wherein the crosslinked layer of polymer comprises a gamma irradiatedcrosslinked layer of polymer.
 5. The bearing of claim 1, wherein thenon-crosslinked layer of polymer is molded to the ceramic component. 6.The bearing of claim 5, wherein the crosslinked layer of polymer ismolded to the non-crosslinked layer of polymer.
 7. The bearing of claim1, wherein the ceramic component comprises a porous ceramic body.
 8. Animplantable orthopaedic bearing, comprising: a ceramic component, afirst layer of polymer secured to the ceramic component, the first layerof polymer being crosslinked to a first degree, and a second layer ofpolymer secured to the first layer of polymer, the second layer ofpolymer being crosslinked to a second degree that is different than thefirst degree.
 9. The bearing of claim 8, wherein the second degree isgreater than the first degree.
 10. The bearing of claim 9, wherein saidsecond layer of polymer has an articulating surface defined therein. 11.The bearing of claim 8, wherein the first layer of polymer is molded tothe second layer of polymer.
 12. The bearing of claim 11, wherein thesecond layer of polymer comprises a gamma irradiated crosslinked layerof polymer.
 13. The bearing of claim 8, wherein the second layer ofpolymer comprises a gamma irradiated crosslinked layer of polymer. 14.The bearing of claim 8, wherein the first layer of polymer is molded tothe ceramic component.
 15. The bearing of claim 14, wherein the secondlayer of polymer is molded to the first layer of polymer.
 16. Thebearing of claim 8, wherein the ceramic component comprises a porousceramic body.
 17. A method of making an implantable orthopaedic bearing,the method comprising the steps of: securing a layer of non-crosslinkedpolymer to a ceramic component, and securing a layer of crosslinkedpolymer to the layer of non-crosslinked polymer.
 18. The method of claim17, wherein both securing steps are performed contemporaneously.
 19. Themethod of claim 17, wherein the step of securing the layer ofnon-crosslinked polymer to the ceramic component is performed prior tothe step of securing the layer of crosslinked polymer to the layer ofnon-crosslinked polymer.
 20. The method of claim 17, wherein the step ofsecuring the layer of non-crosslinked polymer to the ceramic componentis performed after the step of securing the layer of crosslinked polymerto the layer of non-crosslinked polymer.
 21. The method of claim 17,wherein: the step of securing the layer of crosslinked polymer to thelayer of non-crosslinked polymer comprises molding the layer ofcrosslinked polymer to the layer of non-crosslinked polymer to form apolymer composite, and the step of securing the layer of non-crosslinkedpolymer to the ceramic component comprises molding the polymer compositeto the ceramic component.
 22. A method of making an implantableorthopaedic bearing, the method comprising the steps of: securing afirst layer of polymer to a ceramic component, and securing a secondlayer of polymer to the first layer of polymer, the second layer ofpolymer being crosslinked to a greater degree than the first layer. 23.The method of claim 22, wherein both securing steps are performedcontemporaneously.
 24. The method of claim 22, wherein the step ofsecuring the first layer of polymer to the ceramic component isperformed prior to the step of securing the second layer of polymer tothe first layer of polymer.
 25. The method of claim 22, wherein the stepof securing the first layer of polymer to the ceramic component isperformed after the step of securing the second layer of polymer to thefirst layer of polymer.
 26. The method of claim 22, wherein the step ofsecuring the second layer of polymer to the first layer of polymercomprises compression molding the second layer of polymer and the firstlayer of polymer to one another.
 27. The method of claim 22, wherein thestep of securing the first layer of polymer to the ceramic componentcomprises compression molding the first layer of polymer to the ceramiccomponent.